Gallium nitride materials include gallium nitride (GaN) and its alloys such as aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN), and aluminum indium gallium nitride (AlInGaN). These materials are semiconductor compounds that have a relatively wide, direct bandgap which permits highly energetic electronic transitions to occur. Such electronic transitions can result in gallium nitride materials having a number of attractive properties including the ability to efficiently emit blue light, the ability to transmit signals at high frequency, and others. Accordingly, gallium nitride materials are being widely investigated in many microelectronic applications such as transistors, field emitters, and optoelectronic devices.
In many applications, gallium nitride materials are grown on a substrate. However, differences in the properties between gallium nitride materials and substrates can lead to difficulties in growing layers suitable for many applications. For example, gallium nitride (GaN) has a different thermal expansion coefficient (i.e., thermal expansion rate) and lattice constants than many substrate materials including sapphire, silicon carbide and silicon. This differences in thermal expansion and lattice constants may lead to formation of defects including misfit dislocations. Misfit dislocations may have a number of negative effects including degrading overlying semiconductor material regions when the dislocations propagate to those regions, creation of electronic states within energy bands of those regions that negatively effect device performance, and promoting formation of other types of crystal defects (e.g., point defects, line defects and planar defects). These effects can negatively impact device performance.